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De 2I 2, 1941. vL E ROY J, LEISHMAN Re. 21,964

)IC-'RAY STEREOSCOPIC MEANS AND METHOD original Filed oct. 5, 1935 4sheets-shea 1 95. my /00 /a 2! 1941- LE ROYJ. LElsHMAN Re. 21,964

XRAY STEREOSCOPI-G MEANS AND MTHOD original Filed oct. 5, 1935 4Sheets-Sheet 3 /N VEN TOR:

. 2, 1941. LE ROY J. LEISHMAN Re? 21,954

X-RY STEREOSGOPIC MEANS AND METHOD Original Filed Oct. 5, 1955 4Sheets-Sheet 4 Reissued Dec. 2, 1941 UNITED 21,964 x-RAY sTEaEoscorloMEANS AND METHOD Le Roy J. Leishman, Los Angeles, Calif.

Original No.

Serial No.

2,214,621, dated September 10, 1940,

43,688, October 5, 1935. Renewed February 13, 1940. Application forreissue September 10, 1941, Serial No. 410,320

14 Claims.

The invention herein described relates to stereoscopic fluoroscopy andradiography. Some of its objects are: first, to provide practical meansfor varying the distance between the required two sources of X-rays;second, to afford simple means whereby the separate images produced bythe X- rays from these two sources may each be made visible to adifferent eye; third, to make it possible to control the correspondingshutters for both X-ray tubes from a common control; fourth, to providemeans foi*1 producing a second image in the space occupied by the gridlines that cross an X-ray picture or fluoroscopic shadowgraph; andiifth, to provide a simple stereoscope for viewing such stereoscopicpictures. Other objects will appear as the speciiication proceeds.

In the drawings:

Fig. 1 shows diagrammatically an arrangement whereby two fiuoroscopicimages are produced in alternate strips by means of a grid opaque toX-rays and obscured each from a different eye by means of a second gridopaque to ordinary light.

Figs. 2 and 3 illustrate avmodication wherein a vibrating Buckydiaphragm or Lysholm grid causes the two X-ray images to fall inalternate strips during alternate halves of the cycle of the alternating`current operating the X-ray tubes and the grid vibrating mechanism.

Fig. 4 shows a transparent screen of alternate differently coloredrstrips. In one modication of the invention, this colored screen replacesthe grid that is opaque to ordinary light in Fig. 1.

Fig. 5 shows an assembly on which the two X- ray tubes may be mounted,together with the mechanism for operating the shutters and varying thedistance between the tubes. v

Fig. 6 is a side elevation of Fig. 5, with certain parts omitted for thesake of clearness, and showing an X-ray tube mounted in its supports.

Fig. 7 shows part of the control mechanism for the moving partsillustrated in Fig. 5.

Fig. 8 is a plan view of part of the mechanism,

whereby the distance between the tubes is automatically varied inaccordance with the position of the iiuoroscopic screen,- and, of aremote control for the tube shutters.

Fig. 9 is a front' elevation of the outer end of the control mechanismshown in Fig. 8.

Fig. 10 is a front elevation of the back end of the mechanism shown inFig. 8, taken along line -6Bf, Fig. 8, and shows in addition the variouselements whereby motion is transmitted to the movable parts illustratedin Figs. 5 and '1.

Fig. l1 shows diagrammatically a double Kerr cell assembly withadditional parts whereby the right and left eyes may see through theirassociated optical systems during alternate halves of the cycle of theactuating current.

In Fig. 1, A and B are X-ray tubes placed side by side with unlike endstogether. The anode of one tube is connected to the cathode of the otherby wire l, which is in turn connected to the high potential wire 2. Theopposite ends of these tubes, not shown in the figure, are alsoconnected together and to the other side of the high voltage line.X-rays from these tubes fall on the fluorescent screen C through thegrating D, the lines of which are so spaced with relation to the screenC andthe tubes A and B that the rays a from tube A pass between thestrips of the grating D' and fall on the portions of screen C that areshielded by grid Dy from the rays b from tube B, as shown in the figure.E is a grating consisting of lines or strips alternately opaque andtransparent to ordinary light. The spacing of these lines and thedistance of grating E from screen C are such that the right eye R seesthe portion of the screen C made iiuorescent by the rays a from tube A,and the left eye L sees the strips of screen C that are made toiiuoresce by rays b from tube B. Other details of Fig. 1 will beexplained further on in thisspeciflcation.

If a patient to be examined iluoroscopically is placed between the tubesand grid D, the images produced by the X-rays on screen C will beslightly diierent, due to the distance between the targets where theX-rays originate. This difference is well known in stereoscopic X-raywork. Inasmuch as these images lie in alternate strips, the grating Ehides one image from the right eye and the other image from the lefteye, thus permitting each eye to see one image only. Due to thedifference between these images, the eect is stereoscopic, and theshadows appear to be threedimensional objects. The observer thus has thesensation of looking right into the body. The

` grating D may consist of a self-supporting grid of lead or othersubstance opaque to X-rays, or of a sheet of Bakelite, aluminum or othermaterial transparent to X-rays having grooves that are etched, engravedor pressed into the surface and then filled in with a material throughwhich X- rays cannot pass, such as powdered lead in a suitable base. Asatisfactory grid of this nature may also be made by Stringing wirebetween two parallel notched supports, as is done with the warp incertain kinds of weaving.

It is well known in radiography and fluoroscopy that the increasedsharpness of an image pro- Cil similar strips of material withintervening spaces having a greater depth than width. F one of a seriesof magnets or solenoids for attracting the 'iron member G attached tothe grid D2. H is one of a plurality of springs for resisting the actionof the magnets or other similar electrically operated means. The currentthat energizes F is a rectified current originating in the samealternating current source as that which operates the X-ray tubes, asindicated in Fig. 2. When alternating current from wire 93a passesthrough wire 83 in the direction indicated by the arrow, it passesthrough the half-wave rectier 88, then through wire 3I, magnet F, andlwire 92, which connects to 82a, leading to the A. C. source. During theopposite half-cycle of the alternating current, no current will ilowthrough the circuit Just described, because it will be in the wrongdirection to pass through rectifier 88. Alternating vcurrent from wires92a and 93a is also used to operate the high voltage transformer IIIII,whose secondary |05 is connected by wires |06 and IIII to the X-raytubes A and B. Because of the wellknown rectifying action of thesetubes, they operate on opposite halves of the alternating current cycle.It will thus be evident that during one half oi' the alternating currentcycle, F will be inoperative while the rays from one of the tubes passbetween the lead strips of grid D2, leaving dark lines I beneath saidstrips on screen C as indicated in Fig. 2. During the next half cycle, Fwill be energized, thus causing grid D2 sil) to move to the positionshown in Fig. 3, leaving the previously protected parts of the screennow exposed to the other X-ray tube which is now in operation while theilrst tube remains inoperative on this half of the cycle.

'I'he tubes A and B are of course at some distance from screen C, asindicated in Fig. 1, but

they have been placed much closer in Fig. 2 merely to save space; and itshould be understood that the electrical relationship between the tubesand the grid-actuating means, F, is vthe only feature of the tubesintended to be indicated by Fig. 2.

The necessity for rectifying the current to F can be obviated bypolarizing F so that it operates only on alternate halves of the cyclesoi an alter` nating current. Many other electrically operated meanscould be provided to vibrate the grid D2, such as a synchronous motorrevolving an eccentric connected to the grid.

If an object to be X-rayed is placed between an assembly like that ofFig. 2 and a pair of X-ray tubes connected and positioned as shown inFig. 1, and if the current to F is in phase with that which operates thetubes, it is obvious that two diterent shadows will occupy alternatestrips on screen C. By placing a grid like that of E, Fig. 1, in frontof screen C, Fig. 2 or 3, these images may be seen each by the propereye only, and the ef fect will be sterescopic.

Fig. 4 shows a screen of alternate transparent strips of red and greenor other suitable colors. Such a screen may be used as a substitute forscreen E in the previous iigures. The colored lines are of such widththat those of one color will register with the lines of one of theimages on screen C, while the lines of the other image will lie behindthe strips of the other color. If the strips ofthis alternately coloredscreen are red and green and the observer wears spectacles having onered and one green glass, the red strips of the screen will all appearblack to the eye wearing. the green glass and therefore only the imagelying behind the green strips can be seen by this eye. Similarly, theeye wearing the red glass will be able to se the other image only.

It will be obvious that stereoscopic X-ray pictures may be taken inalternate strips on the same plate by means of modifications of theapparatus just described, thus eliminating the necessity of using twoplates with usual plate changers. In such stereoscopic radiography,screen C, Fig. 1 or 22, is replaced by the plate to be exposed.

Such pictures may be viewed by providing a view box with a grating likeE, Fig. 1, or with a transparent screen having alternate strips of adill'erent color, like that illustrated in Fig. 4. In using this latterarrangement, the two eyes must be provided with the colored spectaclesdescribed in a foregoing paragraph.

In Fig. 5, J is a supporting plate which may be A attached to the tubecarriage by means of holes R. Rods K and L are attached to plate J bythe supports M and MI respectively, having connecting screws Yl and YS,respectively. Plates Sl and S2 are suspended between rods K and L bymeans of rollers Q attached to these plates as shown in Figs. 5 and 6.Shaft N, having a righthand threaded portion 3, Fig. 5, and a left-handthreaded portion I, is journaled in the supports O and restrained fromlongitudinal movement by the collars T. Plates SI and S2 carry half nuts5 and 6 respectively, which are adapted to engage threaded portions 3and l respectively of 'the shaft N. 'I'he holes R and R2, Fig. 5, inplates SI and S2 respectively are for mounting X-ray tubes. This may bedone by means of brackets V, Fig, 6, attached to these plates by meansof screws or bolts Y. As shown in this drawing, the tube A is clampedbetween yoke W and support V by means of screws Y2. Plates SI and S2have windows UI and U2 to permit the passage of X- rays. By turningshaft N, by means to be disclosed later, the threaded portions engagehalfnuts 5 and 8, Figs. 5 and 6, causing the plates SI and S2, withX-ray tubes attached thereto, to move to or from a common center,depending upon whether shaft N is turned to the right or left. To limitVthe lateral spread of the X-rays pass ing through windows UI and U2,Fig. 5, shutters ZI, Z2, Z3, and Z4 are movably attached to the platesSI and S2 by means of L-shaped members Il, I2, I3 and I4, attached tothe plates, in the manner indicated in Fig. 6. Shutters ZI and Z2, Fig.5, are provided with arms I5 and I6, respectively, extending toward theleft; and Z4 and Z3 with arms I5a and IBa respectively, extending totheeright. Arms I5 and I6 carry pins I"I and I8 respectively, that ridein slots I9 and 2U respectively, in rocker 2| pivoted on pin 2.2attached to plate Sl. Arms |5a and lia have pins Ila and |8arespectively, that slide in slots I9a and 20a in rocker 2Ia having apivot 22a.

' The outward projections of rockers 2| and 2Ia are pivotally attachedto levers 23 and 23a respectively by pins 24 and 24a. As will be seen inFig. 7, levers 23 and 23a are pivotally joined by pin 25, which slidesvertically in slot 26 in the upwardly extending part of plate J. l Acord 21 attached to pin 25, passes over pulleys P1 and P6 and alsoaround pulley P3, which latter pulley ls attached to shaft 28 journaledin the lateral extension of plate J. If shaft 26 is turned to the right,cord 21 will pull up on pin 25, causing levers 23 and 23a to raise theoutward arm of rockers 2| and 2Ia respectively, Fig. 5. This will movethe upper arms of theseV rockers inwardly, along with pins I1 and |1aand the associated shutters Z| and Z4. This same movement of the rockerswill cause the lower pins I6 and |811 to move outward, thus pullingshutters Z2 and Z3 against the respectively associated shutters ZIand'Z4. Itv

I dlcated by the relative position of these windows with respect to theholes for mounting the tubes, which holes are assumed to besymmetrically arranged in relation to the tubes. More accurate- 1y, thecenter of the opening between shutters ZI and Z2 must be slightly to theright of the focal spot on the target in the 4left tube; and the centerof the opening between shutters Z3 and Z4 must be somewhat to the leftof the focal spot 0n the target in the right tube. This difference isindicated in Fig. 1, in which |0| and ||||a indicate the positions ofthe focal spots on the targets of the left and right tubes respectively.The distance |02 from the centerof the opening between shutters ZI andZ2, and the center of the opening between the other pair of shutters Z3and Z4, is less than the distance ID3 between th focal spots l||I| andIIIIa.

Shutters 23 and 30 operate vertically, and are long enough vto crossboth windows U|and U2. Shutter 29 is attached to cord 3| at 32 and 32a.

Beginning at point 32, cord 3| passes downward and around pulley PI thenup and around pulley P2, thence to the right and around pulley 34, Fig.7, which turns freely on shaft 28. From pulley 34, cord 3| goes to theleft to pulley P3`, and then downward, as shown in Fig. 5, aroundpulleyA P4, thence up and around P5, and finallyvaround pulley P6, andback to 32. 'Ihe lower shutter 33 is attached to cord 3| at points 33and 33a, Fig. 5. If pulley 34 is turned to the right, shutters 29 and 36will close; and they may be opened by turning 34 to the left.

If the frame J is opaque to X- rays, it is necessary to provide it witha window, U3, Fig. 6, to permit'the passage of the rays that emergebetween the shutters. 'I'his window may be wide enough to accommodatethe rays from both tubes, or individual windows may be used. To avoidconfusion with other lines, no window of this type is shown in Fig. 5.

Figures 8, 9, and 10 illustrate, among other things, an automaticmechanism for increasing the distance between the two X-ray tubes as theiiuoroscopic screen is moved away. To plate J is attached two supportingrods, the uppermost of which, 35, is shown in the plan view, Fig. 8. Rod35 passes through holes in arms 36 and 31, which are adapted to movealong 35. Beneath arm 36,

there is another arm '38, shown in Fig. 9. which is a front elevation ofthe parts that lie behind line 33-40, Fig. 8 To these arms is attached aplate 4|, which is fastened to arm 36 by means of bolts 42, passingthrough 36 and tightened in place by nuts 43, Figs. 8 and 9. Plate 4I isfastenedto lower arm 38 by bolts 44 and nuts 45, Fig. 9. 46 is the holein arm 36 which slides along rod 35, Fig. 8, and 41, Fig. 9, is thecorresponding hole in arm 38 which slides along a rod like 35, not shownin Fig. 8 because it lies directly beneath 35.

A shaft 48 passes through arms 36 and 38, Fig. 9, and is held in placeby collars 43 and 50. Beginning at the lower end, this shaft 46supports,- in the order named, one end of lever 5I, spacer 52, pulley53, spacer 54, pulley 55, spacer 56, pulley 51, spacer 58, pulley 59 andspacer 60. These pulleys and lever 5| are all free to turn on shaft 48.Lever 5| is attached to lever 6I, Fig. 8, by pin 62. 'Ihe other end oflever 6| is attached to shaft 63, Fig. 10, to which shaft is alsoattached gear 64. Referring to Fig. 10, which is a front elevation ofthe parts lying behind line 65-66,

Fig. 8, together with additional parts not Ypractical to include in theplan view, it will be seen that shaft 63 is journaled insupports 61 and68 and held in place by collars 69, 69. As the outer end of lever 6|approaches plate J, shaft 63 and gear 64 turn in the direction indicatedby the arrow on gear 64, causing gear 10, shaft 3 and gear 1 to turn inthe direction indicated by the arrow on gear 1, which in turn rotatesgear 6 in the direction of the arrow shown thereon, thus turning shaft Nand bringing the X-ray tubes closer together in the manner previouslyexplained. As the assembly attached to arm 36, Fig. 8, moves away fromplate J, the outward end of lever 6| is pulled away from -plate J bymeans of lever 5|, thus causing the X-ray tubes to nove further apart bymeans of the mechanism illustrated in Figs. 5 and 10.

Although I prefer the above-described automatic means for varying thedistance between the X-ray tubes, it is possible by a, modification to,attach a flexible shaft directlyto shaft N so that the distance betweenthe X-ray tubes may be controlled at the will of the operator from any,

remote point by means of a knob on theopposite end of the flexibleshaft.

The shutters for the tubes may be controlled from the assembly attachedto arm 36, Figs. 8 and 9. Knob 1|, Fig. 8, and pulley 12 are bothattached to shaft 13, journaled in plate 4|. Shaft 13 passes throughknob 14 and tube 15, which is attached to knob 14. Tube 15 passesthrough plate 16 and is attached to pulley 11. Plate 16 is attached toarm 31 and to another arm directly below 31 which therefore doesnot'show in the l Figs. 8 and il,y

drawing. Knobs 1| and 14 control the shutters by means of the cords 21and 3|, which in this case are long enough to extend over a. system ofpulleys, (similar to those used on dental drills)v to pulleys 12 and 11respectively, which are shown in Figs. 8 and 9. In' this modification.pulleys P9 and 34, Fig. '7, are omitted, and the following 12, pulleys53 .and5:3a, Flg.'9, 53h and 53e, Fig; 10,

from whence it passes to pulley P3, Fig. 7. From here back to pulleyP8a, cord 21. follows the course originally described. It will thus beevident that shutters ZI, Z2, Z3, and Z4, Fig. 5, can be controlled byknob 1|, Fig. s, which is attached to pulley 12 by shaft 13. When pulley34, Fig. '1, is eliminated to permit the remote operation of shutters 28and 30, cord 3|, after leaving pulle'y P2, passes over pulley 34a, Fig.10, around pulley 51h, Fig. 10, then around 51a, Figs. 8 and 9, pulleys51., 11, 55, and 55a, Fig. 9, and 55h, Fig. 10, from whence it followsthe course originally described. Inasmuch as pulley 1,1, is connected toknob 14, by tube 15, as shown in Fig. 8, it follows that shutters 29 and3l) may be controlled by knob 14.

If it is not desired to control the vertical and lateral shutters from aremote point, pulley 34, Fig. 7, may instead be connected to a tube andknob like 15 and 14 respectively, Fig. 8, and pulley P8, Fig. '1, may beconnected to shaft 28, which may be extended through the tube andconnected to a knob like 1|. Fig. 8, in a manner well known in the art.

Member 18, Figs. 8 and 9, is fastened between plates 4I and 16 by screws18. Shaft 88 passes through member 18, and to this shaft are attachedarms 8l and 82, by means of screws 83 and 84, respectively. To the otherend of arms `ill and 82, the holder for the uoroscoplc screen has madeit possible, in the past, to use synchronous shutters to block thevision of the right and left eyes alternately to prevent them fromseeing the images intended for the opposite eyes. In addition to newmeans already described for attaining this same end Without the use ofmoving parts, another novel method is to provide each eye with a Kerrcell and associated members and energize the Kerr cells alternately byan A. C. current in phase with that which operates the X-ray tubes. Suchan arrangement is illustrated in Fig. 11, in which 85 and 85a are Kerrcells, 88 and 88a are polarizers for polarizing the incident light rays,and 81 and 81a are analyzers each capable of adjustment with respect toits cooperating polarizer either to transmit or reject the lightpolarized by the associated polarizer. 'I'hese cooperative functions ofpolarizers and analyzers are well-known in the construction ofpolariscopes, which are widely used, and in the Kerr cell units asemployed n television and telephotography. 88 and 88a are rectifyingmeans whereby cells 85 and 85a are operated on alternate halves of thecycle f the same A, C. current. Current from transformer |88, passingthrough lwire 88, in the direction of the arrow, will pass through wire98 and rectifier 88, but will be in the wrong direction to pass through88a. After leaving rectier 88, said current passes through wire 9|, cell85, wire 92 and wire 93 back to theA transformer. During the other halfof the cycle, the current from wire 93 will pass through wire 82a, (inthe direction of the arrow) cell 85a, wire 8Ia, rectifier 88a, wire 98a.and then through wire 88 back to the transformer in an oppositedirection to that during the half of the cycle when 85 was energizedthrough the rectifying action of cell 88. Members 84 and 85, and 84a and85a support the Kerr cell assemblies, which are paired together by meansof brackets 96 and 91, attached to members 95 and 85a by screws 98 and,98a respectively. L and R are the right and left eyes respectively,looking through the cells along lines 98 and 99a respectively.

It is possible, with such Kerr cell assemblies, to arrange the analyzersso that light passes only when the cells are electrically energized, orwhen they are not energized. In the arrangement shown in Fig. 1l, it isimmaterial which adjustment of the analyzers is used, providing bothanalyzers are adjusted the same-that is, so that light passes throughwhichever cell receives the charge, or fails to pass through whicheverone is energized. It will be assumed, however, that the adjustments havebeen xed so that light will pass through the charged cell. When currentpasses through rectifier 88, as is the case during half of the cycle ofthe A. C. current, the left assembly represented by 81, and 88 becomestransparent, and the left eye L is able to see through the assemblyalong line 99; and during the opposite half of the cycle the right eyesees through assembly 81a, 85a and 88a along line 89a. Inasmuch as thesecells are operated by alternating current in phase with that operatingthe X-ray tubes, the polarity is adjusted so that the right and lefteyes see when the left and right tubes, respectively, are operating,thereby carrying out the same objective as that achieved by grating Dand E in Fig. l.

It is obvious that various modifications may be made from theembodiments of the invention herein described without departing from thespirit of the invention.

My claims are:

1. In X-ray apparatus,` a combination including a supporting element;two members movably mounted on said element, each member carrying anX-ray tube and a pair of laterally movable shutters; means for movingsaid members in opposite directions simultaneously; and means for movingthe shutters in each pair simultaneously in opposite directionssimultaneous with the corresponding movement of the shutters in theother pair.

2. In X-ray apparatus, a combination including two X-ray-tube-carryingmembers; means for moving said tube-carrying members in oppositedirections simultaneously; a. pair of shutters movably mounted on eachtube-carrying member; means for moving the shutters in each pairsimultaneously in opposite directions simultaneous with thecorresponding movement of the shutters in the other pair; the distancefrom the adjoining edges of one pair of shutters when closed to theadjoining edges of the other pair of shutters when closed being lessthan the distance from the focal spot on the target of one tube to thefocal spot on the target of the other tube.

3. In X-ray apparatus, a combination including a supporting member; twosupported members each carrying an X-ray tube and a pair of laterallymovable shutters;y manually controllable means for moving said supportedmembers in opposite directions simultaneously; means for moving theshutters in each pair simultaneously in opposite directions simultaneouswith the corresponding movement of the shutters in the other pair; thedistance from the adjoining edges of one pair of shutters when closed tothe adjoining edges of the other pair of shutters when closed being lessthan the distance from the focal spot on the target of one tube to thefocal spot on the target of the other tube.

4. In X-ray apparatus, a combination including: a source of alternatingcurrent; two X-ray tubes adapted `to operate on opposite halves of thecycle of said alternating current; a surface that luoresces when exposedto X-rays; a grid of X-ray resistant strips interposed between saidsurface and said tubes; and electrical means for vibrating said grid insynchronism with thei operation of said tubes; said grid consisting ofparallel strips opaque to X-rays, said strips having a spacingsubstantially equal to their width.

5. In X-ray apparatus, a combination including: two alternatelyoperative sources of X-rays; a surface that fluoresces when exposed toX-rays; a grid comprising parallel strips that are opaque to X-rays,said grid interposed between said sources and said surface; electricalmeans for vibrating said grid; and a grating comprising strips that aretransparent to at least part of the rays ofthe visible spectrumalternating with strips that are substantially opaque to said latterrays; said latter strips adaptedv to register f between said grid andsaid grating.

6. InX-ray apparatus, a combination including: a source of alternatingcurrent; two X-ray tubes adapted to operate on opposite halves of thecycle of said alternating current; a-surface that fluo'resces whenexposed to X-rays, said surface positioned to receive X-rays from saidtubes; and two Kerr cell 4assemblies each comprising a polarizer and ananalyzer; said assemblies adapted to pass light on opposite halves ofthe cycle of said alternating current so that thedluorescence on saidsurface that is caused by the X-rays from one tube may be seen throughone of said assemblies only, and the fluorescence caused by the X-raysfrom the other of said tubesmay be seen through the other assembly only.

7. In X-ray apparatus, a combination includ- 4ing two members, eachcarrying an X-ray tube and a pair 'of laterally movable shutters; afluoroscopic screen; a movably mounted support for said screen adaptedto move in a direction perpendicular to said shutters; and means formoving said members in opposite directions simultaneously, said meansoperated by the movement of said support. i

8. In X-ray apparatus, a combination including a. supporting element;two members movably supported on said element,'each of said memberscarrying an X-ray tube and a pair of laterally movable shutters; a.supporting structure adapted to move toward and from said shutters; ailu- `oroscopic screen carried by said structure; means for moving saidmembers in opposite directions simultaneously, said means operated bythe movement of said structure; means for varying the opening betweeneach of the two pairs of shutters simultaneously, saidshutter-controlling means operable from a manual control carried by saidstructure.

9. In X-ray apparatus, a combination including a supporting element; twomembers movably supported on said element, each of said members carryingan X-ray tube; a structure adapted to move in a direction at rightangles to the direction of movement of said members; a fluorescentscreen mounted on said structure; and automatic means for moving saidmembers in opposite directions simultaneously, said automatic meansoperated by the movement of said structure.

10. In X-ray apparatus, a combination including two X-ray tubes mountedfor relative movement therebetween; two sets of shutters, each setindividual to one of said tubes, said sets mounted for relative movementtherebetween; and means for moving the individual shutters in both setssimultaneously irrespective of the distance between the sets. l

1l. In X-ray apparatus, a combination including: a source of alternatingcurrent; two X-ray tubes adapted to operate on opposite halves of thecycle of said alternating current; a surface that fiuoresces whenexposed to X-rays, said surface positioned to receive X-rays from saidtubes; two devices individual respectively to the right and left eyesand each constructed and arranged to transmit light that has beenpolarized substantially in a given plane; and means interposed between"said screen and said devices for polarizing the light from said screenand transmitting it to said devices on opposite halves of the cycle of.saidvalternating current so thatthe fluorescence on said surface thatis caused by the X-rays from one tube may be seen through one of saiddevices only, and the iluorescence caused by the X-rays from the othertube may be seen through the other device only.

12. In X-ray apparatus, a combination includ- I ing two4 X-ray tubes; astructure movable with i ing two X-ray tubes; means individual to eachtube for limiting the spread of the X-rays emitted thereby; a structuremovable with respect to said tubes; a uorescent screen mounted on saidstructure; and means operable by the movement of said structure forvaryingwthe distance between said tubes and between said rst mentionedmeans.

14. In X-ray apparatus, a combination including two movably mountedX-ray tubes; two sets ofshutters, each set individual to one of saidtubes; a structure movable with respect to said tubes and shutters; aiiuorescent screen mounted on said structure; and means operable by themovement of said structure for moving said tubes in opposite directionssimultaneously and for varying the distance between said sets.

LE ROY- J .LEISHMAN

